Network Working Group F. Baker
Request for Comments: 3175 C. Iturralde
Category: Standards Track F. Le Faucheur
B. Davie
Cisco Systems
September 2001
Aggregation of RSVP for IPv4 and IPv6 Reservations
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This document describes the use of a single RSVP (Resource
ReSerVation Protocol) reservation to aggregate other RSVP
reservations across a transit routing region, in a manner
conceptually similar to the use of Virtual Paths in an ATM
(Asynchronous Transfer Mode) network. It proposes a way to
dynamically create the aggregate reservation, classify the traffic
for which the aggregate reservation applies, determine how much
bandwidth is needed to achieve the requirement, and recover the
bandwidth when the sub-reservations are no longer required. It also
contains recommendations concerning algorithms and policies for
predictive reservations.
1. Introduction
A key problem in the design of RSVP version 1 [RSVP] is, as noted in
its applicability statement, that it lacks facilities for aggregation
of individual reserved sessions into a common class. The use of such
aggregation is recommended in [CSZ], and required for scalability.
The problem of aggregation may be addressed in a variety of ways.
For example, it may sometimes be sufficient simply to mark reserved
traffic with a suitable DSCP (e.g., EF), thus enabling aggregation of
scheduling and classification state. It may also be desirable to
install one or more aggregate reservations from ingress to egress of
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RFC 3175 RSVP Reservation Aggregation September 2001
an "aggregation region" (defined below) where each aggregate
reservation carries similarly marked packets from a large number of
flows. This is to provide high levels of assurance that the end-to-
end requirements of reserved flows will be met, while at the same
time enabling reservation state to be aggregated.
Throughout, we will talk about "Aggregator" and "Deaggregator",
referring to the routers at the ingress and egress edges of an
aggregation region. Exactly how a router determines whether it
should perform the role of aggregator or deaggregator is described
below.
We will refer to the individual reserved sessions (the sessions we
are attempting to aggregate) as "end-to-end" reservations ("E2E" for
short), and to their respective Path/Resv messages as E2E Path/Resv
messages. We refer to the the larger reservation (that which
represents many E2E reservations) as an "aggregate" reservation, and
its respective Path/Resv messages as "aggregate Path/Resv messages".
1.1. Problem Statement: Aggregation Of E2E Reservations
The problem of many small reservations has been extensively
discussed, and may be summarized in the observation that each
reservation requires a non-trivial amount of message exchange,
computation, and memory resources in each router along the way. It
would be nice to reduce this to a more manageable level where the
load is heaviest and aggregation is possible.
Aggregation, however, brings its own challenges. In particular, it
reduces the level of isolation between individual flows, implying
that one flow may suffer delay from the bursts of another.
Synchronization of bursts from different flows may occur. However,
there is evidence [CSZ] to suggest that aggregation of flows has no
negative effect on the mean delay of the flows, and actually leads to
a reduction of delay in the "tail" of the delay distribution (e.g.,
99% percentile delay) for the flows. These benefits of aggregation
to some extent offset the loss of strict isolation.
1.2. Proposed Solution
The solution we propose involves the aggregation of several E2E
reservations that cross an "aggregation region" and share common
ingress and egress routers into one larger reservation from ingress
to egress. We define an "aggregation region" as a contiguous set of
systems capable of performing RSVP aggregation (as defined following)
along any possible route through this contiguous set.
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Communication interfaces fall into two categories with respect to an
aggregation region; they are "exterior" to an aggregation region, or
they are "interior" to it. Routers that have at least one interface
in the region fall into one of three categories with respect to a
given RSVP session; they aggregate, they deaggregate, or they are
between an aggregator and a deaggregator.
Aggregation depends on being able to hide E2E RSVP messages from
RSVP-capable routers inside the aggregation region. To achieve this
end, the IP Protocol Number in the E2E reservation's Path, PathTear,
and ResvConf messages is changed from RSVP (46) to RSVP-E2E-IGNORE
(134) upon entering the aggregation region, and restored to RSVP at
the deaggregator point. These messages are ignored (no state is
stored and the message is forwarded as a normal IP datagram) by each
router within the aggregation region whenever they are forwarded to
an interior interface. Since the deaggregating router perceives the
previous RSVP hop on such messages to be the aggregating router, Resv
and other messages do not require this modification; they are unicast
from RSVP hop to RSVP hop anyway.
The token buckets (SENDER_TSPECs and FLOWSPECS) of E2E reservations
are summed into the corresponding information elements in aggregate
Path and Resv messages. Aggregate Path messages are sent from the
aggregator to the deaggregator(s) using RSVP's normal IP Protocol
Number. Aggregate Resv messages are sent back from the deaggregator
to the aggregator, thus establishing an aggregate reservation on
behalf of the set of E2E flows that use this aggregator and
deaggregator.
Such establishment of a smaller number of aggregate reservations on
behalf of a larger number of E2E reservations yields the
corresponding reduction in the amount of state to be stored and
amount of signalling messages exchanged in the aggregation region.
By using Differentiated Services mechanisms for classification and
scheduling of traffic supported by aggregate reservations (rather
than performing per aggregate reservation classification and
scheduling), the amount of classification and scheduling state in the
aggregation region is even further reduced. It is not only
independent of the number of E2E reservations, it is also independent
of the number of aggregate reservations in the aggregation region.
One or more Diff-Serv DSCPs are used to identify traffic covered by
aggregate reservations and one or more Diff-Serv PHBs are used to
offer the required forwarding treatment to this traffic. There may
be more than one aggregate reservation between the same pair of
routers, each representing different classes of traffic and each
using a different DSCP and a different PHB.
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RFC 3175 RSVP Reservation Aggregation September 20011.3. Definitions
We define an "aggregation region" as a set of RSVP-capable routers
for which E2E RSVP messages arriving on an exterior interface of one
router in the set would traverse one or more interior interfaces (of
this and possibly of other routers in the set) before finally
traversing an exterior interface.
Such an E2E RSVP message is said to have crossed the aggregation
region.
We define the "aggregating" router for this E2E flow as the first
router that processes the E2E Path message as it enters the
aggregation region (i.e., the one which forwards the message from an
exterior interface to an interior interface).
We define the "deaggregating" router for this E2E flow as the last
router to process the E2E Path as it leaves the aggregation region
(i.e., the one which forwards the message from an interior interface
to an exterior interface).
We define an "interior" router for this E2E flow as any router in the
aggregation region which receives this message on an interior
interface and forwards it to another interior interface. Interior
routers perform neither aggregation nor deaggregation for this flow.
Note that by these definitions a single router with a mix of interior
and exterior interfaces may have the capability to act as an
aggregator on some E2E flows, a deaggregator on other E2E flows, and
an interior router on yet other flows.
1.4. Detailed Aspects of Proposed Solution
A number of issues jump to mind in considering this model.
1.4.1. Traffic Classification Within The Aggregation Region
One of the reasons that RSVP Version 1 did not identify a way to
aggregate sessions was that there was not a clear way to classify the
aggregate. With the development of the Differentiated Services
architecture, this is at least partially resolved; traffic of a
particular class can be marked with a given DSCP and so classified.
We presume this model.
We presume that on each link en route, a queue, WDM color, or similar
management component is set aside for all aggregated traffic of the
same class, and that sufficient bandwidth is made available to carry
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the traffic that has been assigned to it. This bandwidth may be
adjusted based on the total amount of aggregated reservation traffic
assigned to the same class.
There are numerous options for exactly which Diff-serv PHBs might be
used for different classes of traffic as it crosses the aggregation
region. This is the "service mapping" problem described in
[RFC2998], and is applicable to situations broader than those
described in this document. Arguments can be made for using either
EF or one or more AF PHBs for aggregated traffic. For example, since
controlled load requires non-TSpec-conformant (policed) traffic to be
forwarded as best effort traffic rather than dropped, it may be
appropriate to use an AF class for controlled load, using the higher
drop preference for non-conformant packets.
In conventional (unaggregated) RSVP operation, a session is
identified by a destination address and optionally a protocol port.
Since data belonging to an aggregated reservation is identified by a
DSCP, the session is defined by the destination address and DSCP.
For those cases where two DSCPs are used (for conformant and non-
conformant packets, as noted above), the session is identified by the
DSCP of conformant packets. In general we will talk about mapping
aggregated traffic onto a DSCP (even if a second DSCP may be used for
non-conformant traffic).
Whichever PHB or PHBs are used to carry aggregated reservations, care
needs to be take in an environment where provisioned Diff-Serv and
aggregated RSVP are used in the same network, to ensure that the
total admitted load for a single PHB does not exceed the link
capacity allocated to that PHB. One solution to this is to reserve
one PHB (or more) strictly for the aggregated reservation traffic
(e.g., AF1 Class) while using other PHBs for provisioned Diff-Serv
(e.g., AF2, AF3 and AF4 Classes).
Inside the aggregation region, some RSVP reservation state is
maintained per aggregate reservation, while classification and
scheduling state (e.g., DSCPs used for classifying traffic) is
maintained on a per aggregate reservation class basis (rather than
per aggregate reservation). For example, if Guaranteed Service
reservations are mapped to the EF DSCP throughout the aggregation
region, there may be a reservation for each aggregator/deaggregator
pair in each router, but only the EF DSCP needs to be inspected at
each interior interface, and only a single queue is used for all EF
traffic.
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RFC 3175 RSVP Reservation Aggregation September 20011.4.2. Deaggregator Determination
The first question is "How do we determine the
Aggregator/Deaggregator pair that are responsible for aggregating a
particular E2E flow through the aggregation region?"
Determination of the aggregator is trivial: we know that an E2E flow
has arrived at an aggregator when its Path message arrives at a
router on an exterior interface and must be forwarded on an interior
interface.
Determination of the deaggregator is more involved. If an SPF
routing protocol, such as OSPF or IS-IS, is in use, and if it has
been extended to advertise information on Deaggregation roles, it can
tell us the set of routers from which the deaggregator will be
chosen. In principle, if the aggregator and deaggregator are in the
same area, then the identity of the deaggregator could be determined
from the link state database. However, this approach would not work
in multi-area environments or for distance vector protocols.
One method for Deaggregator determination is manual configuration.
With this method the network operator would configure the Aggregator
and the Deaggregator with the necessary information.
Another method allows automatic Deaggregator determination and
corresponding Aggregator notification. When the E2E RSVP Path
message transits from an interior interface to an exterior interface,
the deaggregating router must advise the aggregating router of the
correlation between itself and the flow. This has the nice attribute
of not being specific to the routing protocol. It also has the
property of automatically adjusting to route changes. For instance,
if because of a topology change, another Deaggregator is now on the
shortest path, this method will automatically identify the new
Deaggregator and swap to it.
1.4.3. Mapping E2E Reservations Onto Aggregate Reservations
As discussed above, there may be multiple Aggregate Reservations
between the same Aggregator/Deaggregator pair. The rules for mapping
E2E reservations onto aggregate reservations are policy decisions
which depend on the network environment and network administrator's
objectives. Such a policy is outside the scope of this specification
and we simply assume that such a policy is defined by the network
administrator. We also assume that such a policy is somehow
accessible to the Aggregators/Deaggregators but the details of how
this policy is made accessible to Aggregators/Deaggregators (Local
Configuration, COPS, LDAP, etc.) is outside the scope of this
specification.
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RFC 3175 RSVP Reservation Aggregation September 2001
An example of very simple policy would be that all the E2E
reservations are mapped onto a single Aggregate Reservation (i.e.,
single DSCP) between a given pair of Aggregator/Deaggregator.
Another example of policy, which takes into account the Int-Serv
service type requested by the receiver (and signalled in the E2E
Resv), would be where Guaranteed Service E2E reservations are mapped
onto one DSCP in the aggregation region and where Controlled Load E2E
reservations are mapped onto another DSCP.
A third example of policy would be one where the mapping of E2E
reservations onto Aggregate Reservations take into account Policy
Objects (such as information authenticating the end user) which may
be included by the sender in the E2E path and/or by the receiver in
the E2E Resv.
Regardless of the actual policy, a range of options are conceivable
for where the decision to map an E2E reservation onto an aggregate
reservation is taken and how this decision is communicated between
Aggregator and Deaggregator. Both Aggregator and Deaggregator could
be assumed to make such a decision independently. However, this
would either require definition of additional procedures to solve
inconsistent mapping decisions (i.e., Aggregator and Deaggregator
decide to map a given E2E reservation onto different Aggregate
Reservations) or would result in possible undetected misbehavior in
the case of inconsistent decisions.
For simplicity and reliability, we assign the responsibility of the
mapping decision entirely to the Deaggregator. The Aggregator is
notified of the selected mapping by the Deaggregator and follows this
decision. The Deaggregator was chosen rather than the Aggregator
because the Deaggregator is the first to have access to all the
information required to make such a decision (in particular receipt
of the E2E Resv which indicates the requested Int-Serv service type
and includes information signalled by the receiver). This allows
faster operations such as set-up or size adjustment of an Aggregate
Reservation in a number of situations resulting in faster E2E
reservation establishment.
1.4.4. Size of Aggregate Reservations
A range of options exist for determining the size of the aggregate
reservation, presenting a tradeoff between simplicity and
scalability. Simplistically, the size of the aggregate reservation
needs to be greater than or equal to the sum of the bandwidth of the
E2E reservations it aggregates, and its burst capacity must be
greater than or equal to the sum of their burst capacities. However,
if followed religiously, this leads us to change the bandwidth of the
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aggregate reservation each time an underlying E2E reservation
changes, which loses one of the key benefits of aggregation, the
reduction of message processing cost in the aggregation region.
We assume, therefore, that there is some policy, not defined in this
specification (although sample policies are suggested which have the
necessary characteristics). This policy maintains the amount of
bandwidth required on a given aggregate reservation by taking account
of the sum of the bandwidths of its underlying E2E reservations,
while endeavoring to change it infrequently. This may require some
level of trend analysis. If there is a significant probability that
in the next interval of time the current aggregate reservation will
be exhausted, the router must predict the necessary bandwidth and
request it. If the router has a significant amount of bandwidth
reserved but has very little probability of using it, the policy may
be to predict the amount of bandwidth required and release the
excess.
This policy is likely to benefit from introduction of some hysteresis
(i.e., ensure that the trigger condition for aggregate reservation
size increase is sufficiently different from the trigger condition
for aggregate reservation size decrease) to avoid oscillation in
stable conditions.
Clearly, the definition and operation of such policies are as much
business issues as they are technical, and are out of the scope of
this document.
1.4.5. E2E Path ADSPEC update
As described above, E2E RSVP messages are hidden from the Interior
routers inside the aggregation region. Consequently, the ADSPECs of
E2E Path messages are not updated as they travel through the
aggregation region. Therefore, the Deaggregator for a flow is
responsible for updating the ADSPEC in the corresponding E2E Path to
reflect the impact of the aggregation region on the QoS that may be
achieved end-to-end. The Deaggregator should update the ADSPEC of
the E2E Path as accurately as possible.
Since Aggregate Path messages are processed inside the aggregation
region, their ADSPEC is updated by Interior routers to reflect the
impact of the aggregation region on the QoS that may be achieved
within the interior region. Consequently, the Deaggregator should
make use of the information included in the ADSPEC from an Aggregate
Path where available. The Deaggregator may elect to wait until such
information is available before forwarding the E2E Path in order to
accurately update its ADSPEC.
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To maximize the information made available to the Deaggregator,
whenever the Aggregator signals an Aggregate Path, the Aggregator
should include an ADSPEC with fragments for all service types
supported in the aggregation region (even if the Aggregate Path
corresponds to an Aggregate Reservation that only supports a subset
of those service types). Providing this information to the
Deaggregator for every possible service type facilitates accurate and
timely update of the E2E ADSPEC by the Deaggregator.
Depending on the environment and on the policy for mapping E2E
reservations onto Aggregate Reservations, to accurately update the
E2E Path ADSPEC, the Deaggregator may for example:
- update all the E2E Path ADSPEC segments (Default General
Parameters Fragment, Guaranteed Service Fragment, Controlled-Load
Service Fragment) based on the ADSPEC of a single Aggregate Path,
or
- update the E2E Path ADSPEC by taking into account the ADSPEC from
multiple Aggregate Path messages (e.g.,. update the Default
General Parameters Fragment using the "worst" value for each
parameter across all the Aggregate Paths' ADSPECs, update the
Guaranteed Service Fragment using the Guaranteed Service Fragment
from the ADSPEC of the Aggregate Path for the reservation used for
Guaranteed Services).
By taking into account the information contained in the ADSPEC of
Aggregate Path(s) as mentioned above, the Deaggregator should be able
to accurately update the E2E Path ADSPEC in most situations.
However, we note that there may be particular situations where the
E2E Path ADSPEC update cannot be made entirely accurately by the
Deaggregator. This is most likely to happen when the path taken
across the aggregation region depends on the service requested in the
E2E Resv, which is yet to arrive. Such a situation could arise if,
for example:
- The service mapping policy for the aggregation region is such that
E2E reservations requesting Guaranteed Service are mapped to a
different PHB that those requesting Controlled Load service.
- Diff-Serv aware routing is used in the aggregation region, so that
packets with different DSCPs follow different paths (sending them
over different MPLS label switched paths, for example).
As a result, the ADSPEC for the aggregate reservation that supports
guaranteed service may differ from the ADSPEC for the aggregate
reservation that supports controlled load.
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RFC 3175 RSVP Reservation Aggregation September 2001
Assume that the sender sends an E2E Path with an ADSPEC containing
segments for both Guaranteed Services and Controlled Load. Then, at
the time of updating the E2E ADSPEC, the Deaggregator does not know
which service type will actually be requested by the receiver and
therefore cannot know which PHB will be used to transport this E2E
flow and, in turn, cannot pick the right parameter values to factor
in when updating the Default General Parameters Fragment. As
mentioned above, in this particular case, a conservative approach
would be to always take into account the worst value for every
parameter. Regardless of whether this conservative approach is
followed or some simpler approach such as taking into account one of
the two Aggregate Path ADSPEC, the E2E Path ADSPEC will be inaccurate
(over-optimistic or over-pessimistic) for at least one service type
actually requested by the destination.
Recognizing that entirely accurate update of E2E Path ADSPEC may not
be possible in all situations, we recommend that a conservative
approach be taken in such situations (over-pessimistic rather than
over-optimistic) and that the E2E Path ADSPEC be corrected as soon as
possible. In the example described above, this would mean that as
soon as the Deaggregator receives the E2E Resv from the receiver, the
Deaggregator should generate another E2E Path with an accurately
updated ADSPEC based on the knowledge of which aggregate reservation
will actually carry the E2E flow.
1.4.6. Intra-domain Routes
RSVP directly handles route changes, in that reservations follow the
routes that their data follow. This follows from the property that
Path messages contain the same IP source and destination address as
the data flow for which a reservation is to be established. However,
since we are now making aggregate reservations by sending a Path
message from an aggregating to a deaggregating router, the reserved
(E2E) data packets no longer carry the same IP addresses as the
relevant (aggregate) Path message. The issue becomes one of making
sure that data packets for reserved flows follow the same path as the
Path message that established Path state for the aggregate
reservation. Several approaches are viable.
First, the data may be tunneled from aggregator to deaggregator,
using technologies such as IP-in-IP tunnels, GRE tunnels, MPLS
label-switched paths, and so on. These each have particular
advantages, especially MPLS, which allows traffic engineering. They
each also have some cost in link overhead and configuration
complexity.
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If data is not tunneled, then we are depending on a characteristic of
IP best metric routing , which is that if the route from A to Z
includes the path from H to L, and the best metric route was chosen
all along the way, then the best metric route was chosen from H to L.
Therefore, an aggregate path message which crosses a given aggregator
and deaggregator will of necessity use the best path between them.
If this is a single path, the problem is solved. If it is a multi-
path route, and the paths are of equal cost, then we are forced to
determine, perhaps by measurement, what proportion of the traffic for
a given E2E reservation is passing along each of the paths, and
assure ourselves of sufficient bandwidth for the present use. A
simple, though wasteful, way of doing this is to reserve the total
capacity of the aggregate route down each path.
For this reason, we believe it is advantageous to use one of the
above-mentioned tunneling mechanisms in cases where multiple equal-
cost paths may exist.
1.4.7. Inter-domain Routes
The case of inter-domain routes differs somewhat from the intra-
domain case just described. Specifically, best-path considerations
do not apply, as routing is by a combination of routing policy and
shortest AS path rather than simple best metric.
In the case of inter-domain routes, data traffic belonging to
different E2E sessions (but the same aggregate session) may not enter
an aggregation region via the same aggregator interface, and/or may
not leave via the same deaggregator interface. It is possible that
we could identify this occurrence in some central system which sees
the reservation information for both of the apparent sessions, but it
is not clear that we could determine a priori how much traffic went
one way or the other apart from measurement.
We simply note that this problem can occur and needs to be allowed
for in the implementation. We recommend that each such E2E
reservation be summed into its appropriate aggregate reservation,
even though this involves over-reservation.
1.4.8. Reservations for Multicast Sessions
Aggregating reservations for multicast sessions is significantly more
complex than for unicast sessions. The first challenge is to
construct a multicast tree for distribution of the aggregate Path
messages which follows the same path as will be followed by the data
packets for which the aggregate reservation is to be made. This is
complicated by the fact that the path taken by a data packet may
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RFC 3175 RSVP Reservation Aggregation September 2001
depend on many factors such as its source address, the choice of
shared trees or source-specific trees, and the location of a
rendezvous point for the tree.
Once the problem of distributing aggregate Path messages is solved,
there are considerable problems in determining the correct amount of
resources to reserve at each link along the multicast tree. Because
of the amount of heterogeneity that may exist in an aggregate
multicast reservation, it appears that it would be necessary to
retain information about individual E2E reservations within the
aggregation region to allocate resources correctly. Thus, we may end
up with a complex set of procedures for forming aggregate
reservations that do not actually reduce the amount of stored state
significantly for multicast sessions.
As noted above, there are several aspects to RSVP state, and our
approach for unicast aggregates all forms of state: classification,
scheduling, and reservation state. One possible approach to
multicast is to focus only on aggregation of classification and
scheduling state, which are arguably the most important because of
their impact on the forwarding path. That approach is the one
described in the current draft.
1.4.9. Multi-level Aggregation
Ideally, an aggregation scheme should be able to accommodate
recursive aggregation, with aggregate reservations being themselves
aggregated. Multi-level aggregation can be accomplished using the
procedures described here and a simple extension to the protocol
number swapping process.
We can consider E2E RSVP reservations to be at aggregation level 0.
When we aggregate these reservations, we produce reservations at
aggregation level 1. In general, level n reservations may be
aggregated to form reservations at level n+1.
When an aggregating router receives an E2E Path, it swaps the
protocol number from RSVP to RSVP-E2E-IGNORE. In addition, it should
write the aggregation level (1, in this case) in the 2 byte field
that is present (and currently unused) in the router alert option.
In general, a router which aggregates reservations at level n to
create reservations at level n+1 will write the number n+1 in the
router alert field. A router which deaggregates level n+1
reservations will examine all messages with IP protocol number RSVP-
E2E-IGNORE but will process the message and swap the protocol number
back to RSVP only in the case where the router alert field carries
the number n+1. For any other value, the message is forwarded
unchanged. Interior routers ignore all messages with IP protocol
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number RSVP-E2E-IGNORE. Note that only a few bits of the 2 byte
field in the option would be needed, given the likely number of
levels of aggregation.
For IPv6, certain values of the router alert "value" field are
reserved. This specification requires IANA assignment of a small
number of consecutive values for the purpose of recording the
aggregation level.
1.4.10. Reliability Issues
There are a variety of issues that arise in the context of
aggregation that would benefit from some form of explicit
acknowledgment mechanism for RSVP messages. For example, it is
possible to configure a set of routers such that an E2E Path of
protocol type RSVP-E2E-IGNORE would be effectively "black-holed", if
it never reached a router which was appropriately configured to act
as a deaggregator. It could then travel all the way to its
destination where it would probably be ignored due to its non-
standard protocol number. This situation is not easy to detect. The
aggregator can be sure this problem has not occurred if an aggregate
PathErr message is received from the deaggregator (as described in
detail below). It can also be sure there is no problem if an E2E
Resv is received. However, the fact that neither of these events has
happened may only mean that no receiver wishes to reserve resources
for this session, or that an RSVP message loss occurred, or it may
mean that the Path was black-holed. However, if a neighbor-to-
neighbor acknowledgment mechanism existed, the aggregator would
expect to receive an acknowledgment of the E2E Path from the
deaggregator, and would interpret the lack of a response as an
indication that a problem of configuration existed. It could then
refrain from aggregating this particular session. We note that such
a reliability mechanism has been proposed for RSVP in [RFC291] and
propose that it be used here.
1.4.11. Message Integrity and Node Authentication
[RSVP] defines a hop-by-hop authentication and integrity check. The
present specification allows use of this check on Aggregate RSVP
messages and also preserves this check on E2E RSVP messages for E2E
RSVP messages.
Outside the Aggregation Region, any E2E RSVP message may contain an
INTEGRITY object using a keyed cryptographic digest technique which
assumes that RSVP neighbors share a secret. Because E2E RSVP
messages are not processed by routers in the Aggregation Region, the
Aggregator and Deaggregator appear as logical RSVP neighbors of each
other. The Deaggregator is the Aggregator's Next Hop for E2E RSVP
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RFC 3175 RSVP Reservation Aggregation September 2001
messages while the Aggregator is the Deaggregator's Previous Hop.
Consequently, INTEGRITY objects which may appear in E2E RSVP messages
traversing the Aggregation Region are exchanged directly between the
Aggregator and Deaggregator in a manner which is entirely transparent
to the Interior routers. Thus, hop-by-hop integrity checking for E2E
messages over the Aggregation Region requires that the Aggregator and
Deaggregator share a secret. Techniques for establishing that secret
are described in [INTEGRITY].
Inside the Aggregation Region, any Aggregate RSVP message may contain
an INTEGRITY object which assumes that the corresponding RSVP
neighbors inside the Aggregation Region (e.g., Aggregator and
Interior Router, two Interior Routers, Interior Router and
Deaggregator) share a secret.
1.4.12. Aggregated reservations without E2E reservations
Up to this point we have assumed that the aggregate reservation is
established as a result of the establishment of E2E reservations from
outside the aggregation region. It should be clear that alternative
triggers are possible. As discussed in [RFC2998], an aggregate RSVP
reservation can be used to manage bandwidth in a diff-serv cloud even
if RSVP is not used end-to-end.
The simplest example of an alternative configuration is the static
configuration of an aggregated reservation for a certain amount for
traffic from an ingress (aggregator) router to an egress (de-
aggregator) router. This would have to be configured in at least the
system originating the aggregate PATH message (the aggregator). The
deaggregator could detect that the PATH message is directed to it,
and could be configured to "turn around" such messages, i.e., it
responds with a RESV back to the aggregator. Alternatively,
configuration of the aggregate reservation could be performed at both
the aggregator and the deaggregator. As before, an aggregate
reservation is associated with a DSCP for the traffic that will use
the reserved capacity.
In the absence of E2E microflow reservations, the aggregator can use
a variety of policies to set the DSCP of packets passing into the
aggregation region, thus determining whether they gain access to the
resources reserved by the aggregate reservation. These policies are
a matter of local configuration, as usual for a device at the edge of
a diffserv cloud.
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RFC 3175 RSVP Reservation Aggregation September 2001
Note that the "aggregator" could even be a device such as a PSTN
gateway which makes an aggregate reservation for the set of calls to
another PSTN gateway (the deaggregator) across an intervening diff-
serv region. In this case the reservation may be established in
response to call signalling.
From the perspective of RSVP signalling and the handling of data
packets in the aggregation region, these cases are equivalent to the
case of aggregating E2E RSVP reservations. The only difference is
that E2E RSVP signalling does not take place and cannot therefore be
used as a trigger, so some additional knowledge is required in
setting up the aggregate reservation.
2. Elements of Procedure
To implement aggregation, we define a number of elements of
procedure.
2.1. Receipt of E2E Path Message By Aggregating Router
The very first event is the arrival of the E2E Path message at an
exterior interface of an aggregator. Standard RSVP procedures [RSVP]
are followed for this, including onto what set of interfaces the
message should be forwarded. These interfaces comprise zero or more
exterior interfaces and zero or more interior interfaces. (If the
number of interior interfaces is zero, the router is not acting as an
aggregator for this E2E flow.)
Service on exterior interfaces is handled as defined in [RSVP].
Service on interior interfaces is complicated by the fact that the
message needs to be included in some aggregate reservation, but at
this point it is not known which one, because the deaggregator is not
known. Therefore, the E2E Path message is forwarded on the interior
interface(s) using the IP Protocol number RSVP-E2E-IGNORE, but in
every other respect identically to the way it would be sent by an
RSVP router that was not performing aggregation.
2.2. Handling Of E2E Path Message By Interior Routers
At this point, the E2E Path message traverses zero or more interior
routers. Interior routers receive the E2E Path message on an
interior interface and forward it on another interior interface. The
Router Alert IP Option alerts interior routers to check internally,
but they find that the IP Protocol is RSVP-E2E-IGNORE and the next
hop interface is interior. As such, they simply forward it as a
normal IP datagram.
Baker, et al. Standards Track [Page 15]

RFC 3175 RSVP Reservation Aggregation September 20012.3. Receipt of E2E Path Message By Deaggregating Router
The E2E Path message finally arrives at a deaggregating router, which
receives it on an interior interface and forwards it on an exterior
interface. Again, the Router Alert IP Option alerts it to intercept
the message, but this time the IP Protocol is RSVP-E2E-IGNORE and the
next hop interface is an exterior interface.
Before forwarding the E2E Path towards the receiver, the Deaggregator
should update its ADSPEC. This update is to reflect the impact of
the aggregation region onto the QoS to be achieved E2E by the flow.
Such information can be collected by the ADSPEC of Aggregate Path
messages travelling from the Aggregator to the Deaggregator. Thus,
to enable correct updating of the ADSPEC, a deaggregating router may
wait as described below for the arrival of an aggregate Path before
forwarding the E2E Path.
When receiving the E2E Path, depending on the policy for mapping E2E
reservation onto Aggregate Reservations, the Deaggregator may or may
not be in a position to decide which DSCP the E2E flow for the
processed E2E Path is going to be mapped onto, as described above.
If the Deaggregator is in a position to know the mapping at this
point, then the Deaggregator first checks that there is an Aggregate
Path in place for the corresponding DSCP. If so, then the
Deaggregator uses the ADSPEC of this Aggregate Path to update the
ADSPEC of the E2E Path and then forwards the E2E Path towards the
receiver. If not, then the Deaggregator requests establishment of
the corresponding Aggregate Path by sending an E2E PathErr message
with an error code of NEW-AGGREGATE-NEEDED and the desired DSCP
encoded in the DCLASS Object. The Deaggregator may also at the same
time request establishment of an aggregate reservation for other
DSCPs. When receiving the Aggregate Path for the desired DSCP, the
Deaggregator then uses the ADSPEC of this Aggregate Path to update
the ADSPEC of the E2E Path.
If the Deaggregator is not in a position to know the mapping at this
point, then the Deaggregator uses the information contained in the
ADSPEC of one Aggregate Path or of multiple Aggregate Paths to update
the E2E Path ADSPEC. Similarly, if one or more of the necessary
Aggregate Paths is not yet established, the Deaggregator requests
establishment of the corresponding Aggregate Path by sending an E2E
PathErr message with an error code of NEW-AGGREGATE-NEEDED and the
desired DSCP encoded in the respective DCLASS Object. When receiving
the Aggregate Path for the desired DSCP, the Deaggregator then uses
the ADSPEC of this Aggregate Path to update the ADSPEC of the E2E
Path.
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Generating a E2E PathErr message with an error code of NEW-
AGGREGATE-NEEDED should not result in any Path state being removed,
but should result in the aggregating router initiating the necessary
aggregate Path message, as described in the following section.
The deaggregating router changes the E2E Path message's IP Protocol
from RSVP-E2E-IGNORE to RSVP and forwards the E2E Path message
towards its intended destination.
2.4. Initiation of New Aggregate Path Message By Aggregating Router
The aggregating Router is responsible for generating a new Aggregate
Path for a DSCP when receiving a E2E PathErr message with the error
code NEW-AGGREGATE-NEEDED from the deaggregator. The DSCP value to
include in the Aggregate Path Session is found in the DCLASS Object
of the received E2E PathErr message. The identity of the
deaggregator itself is found in the ERROR SPECIFICATION of the E2E
PathErr message. The destination address of the aggregate Path
message is the address of the deaggregating router, and the message
is sent with IP protocol number RSVP.
Existing RSVP procedures specify that the size of a reservation
established for a flow is set to the minimum of the Path SENDER_TSPEC
and the Resv FLOW_SPEC. Consequently, the size of an Aggregate
Reservation cannot be larger than the SENDER_TSPEC included in the
Aggregate Path by the Aggregator. To ensure that Aggregate
Reservations can be sized by the Deaggregator without undesired
limitations, the Aggregating router should always attempt to include
in the Aggregate Path a SENDER_TSPEC which is at least as large as
the size that would actually be required as determined by the
Deaggregator. One method to achieve this is to use a SENDER_TSPEC
which is obviously larger than the highest load of E2E reservations
that may be supported onto this network. Another method is for the
Aggregator to keep track of which flows are mapped onto a DSCP and
always add their E2E Path SENDER_TSPEC into the Aggregate Path
SENDER_TSPEC (and possibly also add some additional bandwidth in
anticipation of future E2E reservations).
The aggregating router is notified of the mapping from an E2E flow to
a DSCP in two ways. First, when the aggregating router receives a
E2E PathErr with error code NEW-AGGREGATE-NEEDED, the Aggregator is
notified that the corresponding E2E flow is (at least temporarily)
mapped onto a given DSCP. Secondly, when the aggregating router
receives an E2E Resv containing a DCLASS Object (as described further
below), the Aggregating Router is notified that the corresponding E2E
flow is mapped onto a given DSCP.
Baker, et al. Standards Track [Page 17]

RFC 3175 RSVP Reservation Aggregation September 20012.5. Handling of E2E Resv Message by Deaggregating Router
Having sent the E2E Path message on toward the destination, the
deaggregator must now expect to receive an E2E Resv for the session.
On receipt, its responsibility is to ensure that there is sufficient
bandwidth reserved within the aggregation region to support the new
E2E reservation, and if there is, then to forward the E2E Resv to the
aggregating router.
The Deaggregating router first makes the final decision of which
Aggregate Reservation (and thus which DSCP) this E2E reservation is
to be mapped onto. This decision is made according to the policy
selected by the network administrator as described above.
If this final mapping decision is such that the Deaggregator can now
make a more accurate update of the E2E Path ADSPEC than done when
forwarding the initial E2E Path, the Deaggregator should do so and
generate a new E2E Path immediately in order to provide the accurate
ADSPEC information to the receiver as soon as possible. Otherwise,
normal Refresh procedures should be followed for the E2E Path.
If no Aggregate Reservation currently exists from the corresponding
aggregating router with the corresponding DSCP, the Deaggregating
router will establish a new Aggregate Reservation as described in the
next section.
If the corresponding Aggregate Reservation exists but has
insufficient bandwidth reserved to accommodate the new E2E
reservation (in addition to all the existing E2E reservations
currently mapped onto it), it should follow the normal RSVP
procedures [RSVP] for a reservation being placed with insufficient
bandwidth to support the reservation. It may also first attempt to
increase the aggregate reservation that is supplying bandwidth by
increasing the size of the FLOW_SPEC that it includes in the
aggregate Resv that it sends upstream. As discussed in the previous
section, the Aggregating Router should ensure that the SENDER_TSPEC
it includes in the Aggregate Path is always in excess of the
FLOW_SPEC that may be requested in the Aggregate Resv by the
Deaggregator, so that the Deaggregator is not unnecessarily prevented
from effectively increasing the Aggregate Reservation bandwidth as
required.
When sufficient bandwidth is available on the corresponding aggregate
reservation, the Deaggregating Router may simply send the E2E Resv
message with IP Protocol RSVP to the aggregating router. This
message should include the DCLASS object to indicate which DSCP the
aggregator must use for this E2E flow. The deaggregator will also
Baker, et al. Standards Track [Page 18]

RFC 3175 RSVP Reservation Aggregation September 2001
add the token bucket from the E2E Resv FLOWSPEC object into its
internal understanding of how much of the Aggregate reservation is in
use.
As discussed above, in order to minimize the occurrence of situations
where insufficient bandwidth is reserved on the corresponding
Aggregate Reservation at the time of processing an E2E Resv, and in
turn to avoid the delay associated with the increase of this
aggregate bandwidth, the Deaggregator MAY anticipate the current
demand and increase the Aggregate Reservations size ahead of actual
requirements by E2E reservations.
2.6. Initiation of New Aggregate Resv Message By Deaggregating Router
Upon receiving an E2E Resv message on an exterior interface, and
having determined the appropriate DSCP for the session according to
the mapping policy, the Deaggregator looks for the corresponding path
state for a session with the chosen DSCP. If aggregate Path state
exists, but no aggregate Resv state exists, the Deaggregator creates
a new aggregate Resv.
If no aggregate Path state exists for the appropriate DSCP, this may
be because the Deaggregator could not decide earlier the final
mapping for this E2E flow and elected to not establish Aggregate Path
state for all DSCPs. In that case, the Deaggregator should request
establishment of the corresponding Aggregate Path by sending a E2E
PathErr with error code of NEW-AGGREGATE-NEEDED and with a DCLASS
containing the required DSCP. This will trigger the Aggregator to
establish the corresponding Aggregate Path. Once the Deaggregator
has determined that the aggregate Path state is established, it
creates a new Aggregate Resv.
The FLOW_SPEC of the new Aggregate Resv is set to a value not smaller
than the requirement of the E2E reservation it is supporting. The
Aggregate Resv is sent toward the aggregator (i.e., to the previous
hop), using the AGGREGATED-RSVP session and filter specifications
defined below. Since the DSCP is in the SESSION object, no DCLASS
object is necessary. The message should be reliably delivered using
the mechanisms in [RFC2961] or, alternatively, the CONFIRM object may
be used, to assure that the aggregate Resv does indeed arrive and is
granted. This enables the deaggregator to determine that the
requested bandwidth is available to allocate to the E2E flows it
supports.
In order to minimize the occurrence of situations where no
corresponding Aggregate Reservation is established at the time of
processing an E2E Resv, and in turn to avoid the delay associated
with the creation of this aggregate reservation, the Deaggregator MAY
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RFC 3175 RSVP Reservation Aggregation September 2001
anticipate the current demand and create the Aggregate Reservation
before receiving E2E Resv messages requiring bandwidth on those
aggregate reservations.
2.7. Handling of Aggregate Resv Message by Interior Routers
The aggregate Resv message is handled in essentially the same way as
defined in [RSVP]. The Session object contains the address of the
deaggregating router (or the group address for the session in the
case of multicast) and the DSCP that has been chosen for the session.
The Filterspec object identifies the aggregating router. These
routers perform admission control and resource allocation as usual
and send the aggregate Resv on towards the aggregator.
2.8. Handling of E2E Resv Message by Aggregating Router
The receipt of the E2E Resv message with a DCLASS Object is the final
confirmation to the aggregating router of the mapping of the E2E
reservation onto an Aggregate Reservation. Under normal
circumstances, this is the only way it will be informed of this
association. It should now forward the E2E Resv to its previous hop,
following normal RSVP processing rules [RSVP].
2.9. Removal of E2E Reservation
E2E reservations are removed in the usual way via PathTear, ResvTear,
timeout, or as the result of an error condition. When they are
removed, their FLOWSPEC information must also be removed from the
allocated portion of the aggregate reservation. This same bandwidth
may be re-used for other traffic in the near future. When E2E Path
messages are removed, their SENDER_TSPEC information must also be
removed from the aggregate Path.
2.10. Removal of Aggregate Reservation
Should an aggregate reservation go away (presumably due to a
configuration change, route change, or policy event), the E2E
reservations it supports are no longer active. They must be treated
accordingly.
2.11. Handling of Data On Reserved E2E Flow by Aggregating Router
Prior to establishment that a given E2E flow is part of a given
aggregate, the flow's data should be treated as traffic without a
reservation by whatever policies prevail for such. Generally, this
will mean being given the same forwarding behavior as best effort
traffic. However, upon establishing that the flow belongs to a given
aggregate, the aggregating router is responsible for marking any
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RFC 3175 RSVP Reservation Aggregation September 2001
related traffic with the correct DSCP and forwarding it in the manner
appropriate to traffic on that reservation. This may imply
forwarding it to a given IP next hop, or piping it down a given link
layer circuit, tunnel, or MPLS label switched path.
The aggregator is responsible for performing per-reservation policing
on the E2E flows that it is aggregating. The aggregator performs
metering of traffic belonging to each reservation to assess
compliance to the token bucket for the corresponding E2E reservation.
Packets which are assessed in compliance are forwarded as mentioned
above. Packets which are assessed out of compliance must be either
dropped, reshaped or marked to a different DSCP. The detailed
policing behavior is an aspect of the service mapping described in
[RFC2998].
2.12. Procedures for Multicast Sessions
Because of the difficulties of aggregating multicast sessions
described above, we focus on the aggregation of scheduling and
classification state in the multicast case. The main difference
between the multicast and unicast cases is that rather than sending
an aggregate Path message to the unicast address of a single
deaggregating router, in the multicast case we send the "aggregate"
Path message to the same group address as the E2E session. This
ensures that the aggregate Path message follows the same route as the
E2E Path. This difference between unicast and multicast is reflected
in the Session objects defined below. A consequence of this approach
is that we continue to have reservation state per multicast session
inside the aggregation region.
A further challenge arises in multicast sessions with heterogeneous
receivers. Consider an interior router which must forward packets
for a multicast session on two interfaces, but has only received a
reservation request on one of those interfaces. It receives packets
marked with the DSCP chosen for the aggregate reservation. When
sending them out the interface which has no installed reservation, it
has the following options:
a) remark those packets to best effort before sending them out the
interface;
b) send the packets out the interface with the DSCP chosen for the
aggregate reservation.
The first approach suffers from the drawback that it requires nMF
classification at an interior router in order to recognize the flows
whose packets must be demoted. The second approach requires over-
reservation of resources on the interface on which no reservation was
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RFC 3175 RSVP Reservation Aggregation September 2001
received. In the absence of such over-reservation, the packets sent
with the "wrong" DSCP would be able to degrade the service
experienced by packets using that DSCP legitimately.
To make MF classification acceptable in an interior router, it may be
possible to treat the case of heterogeneous flows as an exception.
That is, an interior router only needs to be able to recognize those
individual microflows that have heterogeneous resource needs on the
outbound interfaces of this router.
3. Protocol Elements3.1. IP Protocol RSVP-E2E-IGNORE
This specification requires the assignment of a protocol type RSVP-
E2E-IGNORE, whose number is at this point 134. This is used only on
E2E messages which require a router alert (Path, PathTear, and
ResvConf), and signifies that the message must be treated one way
when destined to an interior interface, and another way when destined
to an exterior interface. The protocol type is swapped by the
Aggregator from RSVP to RSVP-E2E-IGNORE in E2E Path, PathTear, and
ResvConf messages when they enter the Aggregation Region. The
protocol type is swapped back by the Deaggregator from RSVP-E2E-
IGNORE to RSVP in such E2E messages when they exit the Aggregation
Region.
3.2. Path Error Code
A PathErr code NEW-AGGREGATE-NEEDED is required. This value does not
signify that a fatal error has occurred, but that an action is
required of the aggregating router to avoid an error condition in the
near future.
3.3. SESSION Object
The SESSION object contains two values: the IP Address of the
aggregate session destination, and the DSCP that it will use on the
E2E data the reservation contains. For unicast sessions, the session
destination address is the address of the deaggregating router. For
multicast sessions, the session destination is the multicast address
of the E2E session (or sessions) being aggregated. The inclusion of
the DSCP in the session allows for multiple sessions toward the same
address to be distinguished by their DSCP and queued separately. It
also provides the means for aggregating scheduling and classification
state. In the case where a session uses a pair of PHBs (e.g., AF11
and AF12), the DSCP used should represent the numerically smallest
PHB (e.g., AF11). This follows the same naming convention described
in [BRIM].
Baker, et al. Standards Track [Page 22]

RFC 3175 RSVP Reservation Aggregation September 2001
o IP6 SENDER_TEMPLATE object: Class = SENDER_TEMPLATE,
C-Type = RSVP-AGGREGATE-IP6
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IPv6 Aggregator Address (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
3.5. FILTER_SPEC Object
The FILTER_SPEC object identifies the aggregating router for the
aggregate reservation, and is syntactically identical to the
SENDER_TEMPLATE object.
4. Policies and Algorithms For Predictive Management Of Blocks Of Bandwidth
The exact policies used in determining how much bandwidth should be
allocated to an aggregate reservation at any given time are beyond
the scope of this document, and may be proprietary to the service
provider in question. However, here we explore some of the issues
and suggest approaches.
In short, the ideal condition is that the aggregate reservation
always has enough resources to allocate to any E2E reservation that
requires its support, and never takes too much. Simply stated, but
more difficult to achieve. Factors that come into account include
significant times in the diurnal cycle: one may find that a large
number of people start placing calls at 8:00 AM, even though the hour
from 7:00 to 8:00 is dead calm. They also include recent history: if
more people have been placing calls recently than have been
finishing them, a prediction of the necessary bandwidth a few moments
hence may call for more bandwidth than is currently allocated.
Likewise, at the end of a busy period, we may find that the trend
calls for declining reservation amounts.
We recommend a policy something along this line. At any given time,
one should expect that the amount of bandwidth required for the
aggregate reservation is the larger of the following:
(a) a requirement known a priori, such as from history of the diurnal
cycle at a particular week day and time of day, and
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RFC 3175 RSVP Reservation Aggregation September 2001
(b) the trend line over recent history, with 90 or 99% statistical
confidence.
We further expect that changes to that aggregate reservation would be
made no more often than every few minutes, and ideally perhaps on
larger granularity such as fifteen minute intervals or hourly. The
finer the granularity, the greater the level of signaling required,
while the coarser the granularity, the greater the chance for error,
and the need to recover from that error.
In general, we expect that the aggregate reservation will not ever
add up to exactly the sum of the reservations it supports, but rather
will be an integer multiple of some block reservation size, which
exceeds that value.
5. Security Considerations
Numerous security issues pertain to this document; for example, the
loss of an aggregate reservation to an aggressor causes many calls to
operate unreserved, and the reservation of a great excess of
bandwidth may result in a denial of service. However, these issues
are not confined to this extension: RSVP itself has them. We believe
that the security mechanisms in RSVP address these issues as well.
One security issue specific to RSVP aggregation involves the
modification of the IP protocol number in RSVP Path messages that
traverse an aggregation region. If that field were maliciously
modified in a Path message, it would cause the message to be ignored
by all subsequent devices on its path, preventing reservations from
being made. It could even be possible to correct the value before it
reached the receiver, making it difficult to detect the attack. In
theory, it might also be possible for a node to modify the IP
protocol number for non-RSVP messages as well, thus interfering with
the operation of other protocols.
One way to mitigate the risks of malicious modification of the IP
protocol number is to use an IPSEC authentication header, which would
ensure that malicious modification of the IP header is detected.
This is a desirable approach but imposes some administrative burden
in the form of key management for authentication purposes.
It is RECOMMENDED that implementations of this specification only
support modification of the IP protocol number for RSVP Path,
PathTear, and ResvConf messages. That is, a general facility for
modification of the IP protocol number SHOULD NOT be made available.
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RFC 3175 RSVP Reservation Aggregation September 2001
Network operators deploying routers with RSVP aggregation capability
should be aware of the risks of inappropriate modification of the IP
protocol number and should take appropriate steps (physical security,
password protection, etc.) to reduce the risk that a router could be
configured by an attacker to perform malicious modification of the
protocol number.
6. IANA ConsiderationsSection 1.2 proposes a new protocol type, RSVP-E2E-IGNORE, which is
used to identify a message that routers in the network core will see;
further processing of such messages may or may not be required,
depending on the egress interface type, as described in Section 1.2.
The IANA assigned IP protocol number 134, in accordance with
[RFC2780], meeting the Standards Track publication criterion.
Section 1.4.9 describes the manner in which the Router Alert is used
in the context of this specification, which is essentially a simple
counter of the depth of nesting of aggregation. The IPv4 Router
Alert [RFC2113] has the option simply to ask the router to look at
the protocol type of the intercepted datagram and decide what to do
with it; the parameter is additional information to that decision.
The IPv6 Router Alert [RFC2711] turns the parameter into an option
sub-type. As a result, the IPv6 router alert option may not be used
algorithmically in the context of the protocol in question. The IANA
assigned a block of 32 values (3-35, "Aggregated Reservation Nesting
Level") which we may map to nesting depths 0..31, hoping that 32
levels is enough.
Section 3.2 discusses a new, required path error code. The IANA has
assigned RSVP Parameters Error Code 26 to NEW-AGGREGATE-NEEDED.
Sections 3.3, 3.4, and 3.5 describe extensions to three object
classes: Session, Filter Specification, and Sender Template. The
IANA has assigned two new common C-Types to be specified for the
aggregator's address. RSVP-AGGREGATE-IP4 is C-Type 9 and RSVP-
AGGREGATE-IP6 is C-Type 10. In adding these C-types to IANA RSVP
Class Names, Class Numbers and Class Types registry, the same
numbering for them is used in all three Classes, as is done for IPv4
and IPv6 address tuples in [RSVP].
Baker, et al. Standards Track [Page 26]

RFC 3175 RSVP Reservation Aggregation September 20017. Acknowledgments
The authors acknowledge that published documents and discussion with
several people, notably John Wroclawski, Steve Berson, and Andreas
Terzis materially contributed to this document. The design is
influenced by the RSVP tunnels document [TERZIS].
Baker, et al. Standards Track [Page 27]

RFC 3175 RSVP Reservation Aggregation September 2001
(1) Aggregator forwards E2E Path into aggregation region after
modifying its IP Protocol Number to RSVP-E2E-IGNORE
(2) Let's assume no Aggregate Path exists. To be able to accurately
update the ADSPEC of the E2E Path, the Deaggregator needs the
ADSPEC of Aggregate PATH. In this example the Deaggregator
elects to instruct the Aggregator to set up Aggregate Path
states for the two supported DSCPs by sending a New-Agg-Needed
PathErr code for each DSCP.
(3) The Aggregator follows the request from the Deaggregator and
signals an Aggregate Path for both DSCPs.
(4) The Deaggregator takes into account the information contained in
the ADSPEC from both Aggregate Path and updates the E2E Path
ADSPEC accordingly. The Deaggregator also modifies the E2E Path
IP Protocol Number to RSVP before forwarding it.
(5) In this example, the Deaggregator elects to immediately proceed
with establishment of Aggregate Reservations for both DSCPs. In
effect, the Deaggregator can be seen as anticipating the actual
demand of E2E reservations so that resources are available on
Aggregate Reservations when the E2E Resv requests arrive in
order to speed up establishment of E2E reservations. Assume
also that the Deaggregator includes the optional Resv Confirm
Request in these Aggregate Resv.
(6) The Aggregator merely complies with the received ResvConfirm
Request and returns the corresponding Aggregate ResvConfirm.
(7) The Deaggregator has explicit confirmation that both Aggregate
Resv are established.
(8) On receipt of the E2E Resv, the Deaggregator applies the mapping
policy defined by the network administrator to map the E2E Resv
onto an Aggregate Reservation. Let's assume that this policy is
such that the E2E reservation is to be mapped onto the Aggregate
Reservation with DSCP=x. The Deaggregator knows that an
Aggregate Reservation is in place for the corresponding DSCP
since (7). The Deaggregator performs admission control of the
E2E Resv onto the Aggregate Resv for DSCP=x. Assuming that the
Aggregate Resv for DSCP=x had been established with sufficient
bandwidth to support the E2E Resv, the Deaggregator adjusts its
counter tracking the unused bandwidth on the Aggregate
Reservation and forwards the E2E Resv to the Aggregator
including a DCLASS object conveying the selected mapping onto
DSCP=x.
Baker, et al. Standards Track [Page 29]

RFC 3175 RSVP Reservation Aggregation September 2001
(9) The Aggregator records the mapping of the E2E Resv onto DSCP=x.
The Aggregator removes the DCLASS object and forwards the E2E
Resv towards the sender.
APPENDIX 2: Example Signalling Flow For Subsequent E2E Flow Without
Reservation Resizing
This Appendix does not provide additional specification. It only
illustrates the specification detailed above through a possible flow
of RSVP signalling messages involved in the successful establishment
of a unicast E2E reservation which follows other E2E reservations
between a given pair of Aggregator/Deaggregator. This flow could be
imagined as following the flow of messages illustrated in Appendix 1.
Aggregator Deaggregator
E2E Path
---------------->
(10)
E2E Path
------------------------------->
(11)
E2E Path
----------->
E2E Resv
<-----------
(12)
E2E Resv (DCLASS=x)
<-----------------------------
(13)
E2E Resv
<---------------
(10) Aggregator forwards E2E Path into aggregation region after
modifying its IP Protocol Number to RSVP-E2E-IGNORE
(11) Because previous E2E reservations have been established, let's
assume that Aggregate Path exists for all supported DSCPs. The
Deaggregator takes into account the information contained in the
ADSPEC from the Aggregate Paths and updates the E2E Path ADSPEC
accordingly. The Deaggregator also modifies the E2E Path IP
Protocol Number to RSVP before forwarding it.
(12) On receipt of the E2E Resv, the Deaggregator applies the mapping
policy defined by the network administrator to map the E2E Resv
onto an Aggregate Reservation. Let's assume that this policy is
such that the E2E reservation is to be mapped onto the Aggregate
Reservation with DSCP=x. Because previous E2E reservations have
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RFC 3175 RSVP Reservation Aggregation September 2001
been established, let's assume that an Aggregate Reservation is
in place for DSCP=x. The Deaggregator performs admission
control of the E2E Resv onto the Aggregate Resv for DSCP=x.
Assuming that the Aggregate Resv for DSCP=x has sufficient
unused bandwidth to support the new E2E Resv, the Deaggregator
then adjusts its counter tracking the unused bandwidth on the
Aggregate Reservation and forwards the E2E Resv to the
Aggregator including a DCLASS object conveying the selected
mapping onto DSCP=x.
(13) The Aggregator records the mapping of the E2E Resv onto DSCP=x.
The Aggregator removes the DCLASS object and forwards the E2E
Resv towards the sender.
APPENDIX 3: Example Signalling Flow For Subsequent E2E Flow With
Reservation Resizing
This Appendix does not provide additional specification. It only
illustrates the specification detailed above through a possible flow
of RSVP signalling messages involved in the successful establishment
of a unicast E2E reservation which follows other E2E reservations
between a given pair of Aggregator/Deaggregator. This flow could be
imagined as following the flow of messages illustrated in Appendix 2.
Baker, et al. Standards Track [Page 31]

RFC 3175 RSVP Reservation Aggregation September 2001
Aggregator Deaggregator
E2E Path
---------------->
(14)
E2E Path
------------------------------->
(15)
E2E Path
----------->
E2E Resv
<-----------
(16)
AggResv (DSCP=x, increased Bw)
<-------------------------------
(17)
AggResvConfirm (DSCP=x, increased Bw)
------------------------------>
(18)
E2E Resv (DCLASS=x)
<-----------------------------
(19)
E2E Resv
<---------------
(14) Aggregator forwards E2E Path into aggregation region after
modifying its IP Protocol Number to RSVP-E2E-IGNORE
(15) Because previous E2E reservations have been established, let's
assume that Aggregate Path exists for all supported DSCPs. The
Deaggregator takes into account the information contained in the
ADSPEC from the Aggregate Paths and updates the E2E Path ADSPEC
accordingly. The Deaggregator also modifies the E2E Path IP
Protocol Number to RSVP before forwarding it.
(16) On receipt of the E2E Resv, the Deaggregator applies the mapping
policy defined by the network administrator to map the E2E Resv
onto an Aggregate Reservation. Let's assume that this policy is
such that the E2E reservation is to be mapped onto the Aggregate
Reservation with DSCP=x. Because previous E2E reservations have
been established, let's assume that an Aggregate Reservation is
in place for DSCP=x. The Deaggregator performs admission
control of the E2E Resv onto the Agg Resv for DSCP=x. Let's
assume that the Aggregate Resv for DSCP=x does NOT have
sufficient unused bandwidth to support the new E2E Resv. The
Baker, et al. Standards Track [Page 32]

RFC 3175 RSVP Reservation Aggregation September 2001
Deaggregator then attempts to increase the Aggregate Reservation
bandwidth for DSCP=x by sending a new Aggregate Resv with an
increased bandwidth sufficient to accommodate all the E2E
reservations already mapped onto that Aggregate reservation plus
the new E2E reservation plus possibly some additional spare
bandwidth in anticipation of additional E2E reservations to
come. Assume also that the Deaggregator includes the optional
Resv Confirm Request in these Aggregate Resv.
(17) The Aggregator merely complies with the received ResvConfirm
Request and returns the corresponding Aggregate ResvConfirm.
(18) The Deaggregator has explicit confirmation that the Aggregate
Resv has been successfully increased. The Deaggregator performs
again admission control of the E2E Resv onto the increased
Aggregate Reservation for DSCP=x. Assuming that the increased
Aggregate Reservation for DSCP=x now has sufficient unused
bandwidth and resources to support the new E2E Resv, the
Deaggregator then adjusts its counter tracking the unused
bandwidth on the Aggregate Reservation and forwards the E2E Resv
to the Aggregator including a DCLASS object conveying the
selected mapping onto DSCP=x.
(19) The Aggregator records the mapping of the E2E Resv onto DSCP=x.
The Aggregator removes the DCLASS object and forwards the E2E
Resv towards the sender.
References
[CSZ] Clark, D., S. Shenker, and L. Zhang, "Supporting Real-
Time Applications in an Integrated Services Packet
Network: Architecture and Mechanism," in Proc.
SIGCOMM'92, September 1992.
[IP] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[HOSTREQ] Braden, R., "Requirements for Internet hosts -
communication layers", STD 3, RFC 1122, October 1989.
[DSFIELD] Nichols, K., Blake, S., Baker, F. and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, December
1998.
[PRINCIPLES] Carpenter, B., "Architectural Principles of the
Internet", RFC 1958, June 1996.
Baker, et al. Standards Track [Page 33]

RFC 3175 RSVP Reservation Aggregation September 2001
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Baker, et al. Standards Track [Page 36]